Titanium alloy

Abstract

A titanium base alloy powder is formed by subsurface reduction of a chloride vapor with a molten alkali metal or molten alkaline earth metal to form reaction products comprising pre-alloy particles and a salt of the alkali metal or the alkaline earth metal. A majority of the pre-alloy particles have a composition of at least 50% by weight of titanium, about 5.38% to 6.95% by weight of aluminum, and about 3% to 5% by weight of vanadium. The pre-alloy particles are recovered from the reaction products to produce a titanium base alloy powder containing less than about 200 ppm alkali or alkaline earth metal.

Claims

1. A method of forming a titanium base alloy powder, the method comprising: subsurface reduction of a chloride vapor with a molten alkali metal or molten alkaline earth metal to form reaction products comprising pre-alloy particles and a salt of the alkali metal or the alkaline earth metal, a majority of the pre-alloy particles having a composition of at least 50% by weight of titanium, 5.38% or more by weight of aluminum, and 3.45% or more by weight of vanadium, wherein the total amount of aluminum and vanadium is less than about 20% by weight; and recovering the pre-alloy particles from the reaction products to produce a titanium base alloy powder containing less than about 200 ppm alkali or alkaline earth metal and a surface area as determined by BET analysis of at least about 3 square meters per gram after distillation of the powder at temperatures between about 500 C. and about 575 C. for about 8 to about 12 hours.

2. The method of claim 1, wherein the titanium base alloy powder meets ASTM B265 grade 5 chemical specifications.

3. The method of claim 1, wherein the alkali metal is Na, K or mixtures thereof and the alkaline earth metal is Mg, Ca, Ba or mixtures thereof.

4. The method of claim 1, wherein the titanium alloy powder is in agglomerates having an average mean diameter as measured by sieve analysis greater than about 50 microns.

5. The method of claim 1, wherein the titanium alloy powder contains less than about 100 ppm sodium, magnesium, calcium.

6. The method of claim 1, further comprising forming the titanium alloy powder into a sintered product.

7. A method of forming a titanium base alloy powder, the method comprising: subsurface reduction of a chloride vapor with a molten alkali metal or molten alkaline earth metal to form reaction products comprising pre-alloy particles and a salt of the alkali metal or the alkaline earth metal, a majority of the pre-alloy particles having a composition of at least 50% by weight of titanium, about 5.38% to 6.95% by weight of aluminum, and about 3% to 5% by weight of vanadium; and recovering the pre-alloy particles from the reaction products to produce a titanium base alloy powder containing less than about 200 ppm alkali or alkaline earth metal and a surface area as determined by BET analysis of at least about 3 square meters per gram after distillation of the powder at temperatures between about 500 C. and about 575 C. for about 8 to about 12 hours.

8. The method of claim 7, wherein the titanium base alloy powder meets ASTM B265 grade 5 chemical specifications.

9. The method of claim 7, wherein the alkali metal is Na, K or mixtures thereof and the alkaline earth metal is Mg, Ca, Ba or mixtures thereof.

10. The method of claim 7, wherein the titanium alloy powder is in agglomerates having an average mean diameter as measured by sieve analysis greater than about 50 microns.

11. The method of claim 7, wherein the titanium alloy powder contains less than about 100 ppm sodium, magnesium, calcium.

12. The method of claim 7, further comprising forming the titanium alloy powder into a sintered product.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawings a preferred embodiment thereof, from an inspection of which, when considered in connection with the following description, the invention, its construction and operation, and many of its advantages should be readily understood and appreciated.

(2) FIG. 1 is a SEM of CP powder made by the hydride-dehydride method;

(3) FIG. 2 is a SEM of CP powder made by the spheridization method;

(4) FIG. 3 is a SEM of CP powder from the Hunter Process;

(5) FIG. 4-6 are SEMs of Armstrong CP distilled, dried and passivated;

(6) FIG. 7-9 are SEMs of Armstrong CP distilled, dried, passivated and held at 750 C. for 48 hours; and

(7) FIG. 10-12 are SEMs of Armstrong 6/4 distilled, dried, passivated and held at 750 C. for 48 hours.

DETAILED DESCRIPTION OF THE INVENTION

(8) As used herein, a titanium base alloy means any alloy having 50% or more by weight titanium. Although 6/4 is used as a specific example, other titanium base alloys are included in this invention. As seen from the previous discussion, Armstrong CP titanium powder is different from spheridized titanium powder and from hydride-dehydride titanium powder in both morphology and packing fraction or tap density. There are also differences in certain of the chemical constituents. For instance, Armstrong CP titanium powder has sodium present in the 400-700 ppm range while spheridized and hydride-dehydride powder should have none or only trace amounts. Armstrong CP titanium has little chloride concentration, on the order of <50 ppm, while Hunter fines have much larger concentrations of chlorides, on the order of 0.12-0.15 wt. %.

(9) The equipment used to produce the 6/4 alloy is substantially as disclosed in the aforementioned patents disclosing the Armstrong Process with the exception that instead of only having a titanium tetrachloride boiler 22 as illustrated in those patents, there is also a vanadium tetrachloride boiler and an aluminum trichloride boiler which are connected to the reaction chamber by suitable valves. The piping acts as a manifold so that the gases are completely mixed as they enter the reaction chamber and are introduced subsurface to the flowing liquid sodium. It was determined during production of the 6/4 alloy that aluminum trichloride is corrosive and required special materials not required for handling either titanium tetrachloride or vanadium tetrachloride. Therefore, Hastelloy C-276 was used for the aluminum trichloride boiler and the piping to the reaction chamber.

(10) During most of the runs the steady state temperature of the reactor was maintained at about 400 C. by the use of sufficient excess sodium. Other operating conditions for the production of the alloy were as follows:

(11) A device similar to that described in the incorporated Armstrong patents was used except that a VCl.sub.4 boiler and AlCl.sub.3 boiler were provided and both gases were fed into the line feeding TiCl.sub.4 into the liquid Na. The boiler pressures and system parameters are listed hereafter.

EXPERIMENTAL PROCEDURE

(12) TiCl.sub.4 Boiler Pressure=500 kPa

(13) VCl.sub.4 Boiler Pressure=630 kPa

(14) AlCl.sub.3 Boiler Pressure=830 kPa

(15) Inlet Na temperature=240 C.

(16) Reactor Outlet Temperature=510 C.

(17) Na Flowrate=40 kg/min

(18) TiCl.sub.4 Flowrate=2.6 kg/min

(19) For this specific experiment, a 7/32 nozzle was used in the reactor to meter the mix of metal chloride vapors. A 0.040 nozzle was used to meter the AlCl.sub.3 and a 0.035 nozzle was used to meter the VCl.sub.4 into the TiCl.sub.4 stream. The reactor was operated for approximately 250 seconds injecting approximately 11 kg of TiCl.sub.4. The salt and titanium alloy solids were captured on a wedge wire filter and free sodium metal was drained away. The product cake containing titanium alloy, sodium chloride and sodium was distilled at approximately 100 milli-torr at 550 to 575 C. vessel wall temperatures for 20 hours. Once all the sodium metal was removed via distillation, the trap was re-pressurized with argon gas and heated to 750 C. and held at temperature for 48 hours. The vessel containing the salt and titanium alloy cake was cooled and the cake was passivated with a 0.7 wt % oxygen/argon mixture. After passivation, the cake was washed with deionized water and subsequently dried in a vacuum oven at less than 100 C.

(20) Table 2 below sets forth a chemical analysis of various runs for 6/4 alloy from an experimental loop running the Armstrong Process.

(21) TABLE-US-00002 TABLE 2 Ti 6/4 FROM EXPERIMENTAL LOOP Run Size Oxygen Sodium Nitrogen Hydrogen Chloride Vanadium Aluminum Carbon Iron N-269- * 0.187 0.019 0.006 0.0029 0.001 5.58 5.58 0.019 0.014 N-269- + 0.113 0.0015 0.008 0.003 0.001 5.33 5.38 0.03 0.021 N-269- + 0.128 0.0006 0.005 0.0037 0.001 5.84 5.47 0.039 0.02 N-271- + 0.124 0.002 0.001 0.0066 0.0016 4.87 6.95 0.033 0.037 N-276 + 0.111 0.0018 4.44 6.04 N-276 + 0.121 0.0018 0.005 0.0043 0.0005 4.12 6.35 0.012 0.016 N-276 + 0.131 0.0019 0.003 0.0057 0.0011 4.03 5.67 0.012 0.016 N-276 + 0.169 0.0026 4.1 6.02 N-276 + 0.128 0.0015 0.003 0.0042 0.0005 3.8 6.02 0.012 0.019 N-277 + 0.155 0.0018 0.003 0.0053 0.0006 3.45 5.73 0.014 0.015 N-277 + 0.135 0.0023 3.49 5.49 N-276 * 0.121 0.0041 0.005 0.0052 0.0005 4.31 6.53 0.02 0.015 N-276 * 0.134 0.0075 3.81 5.92 N-276 * 0.175 0.014 0.012 0.0066 0.0005 3.96 6.01 N-276 * 0.187 0.046 0.007 0.0081 0.0005 3.95 6.05 N-277 * 0.141 0.0022 0.004 0.0038 0.0026 3.65 5.42 Mean 0.14125 0.0069125 0.0051667 0.00495 0.00095 4.295625 5.914375 0.0212222 0.0192222 Stand dev. 0.0253811 0.0116064 0.0028868 0.0015952 0.000626 0.7343838 0.4335892 0.0102808 0.0071024 * = BULK + = SMALL

(22) As seen from the above Table 2, the sodium levels for 6/4 are very low on the order of 69 ppm and for certain runs, sodium levels have been undetectable. This result was unexpected because over two hundred runs of CP titanium have been made using the Armstrong Process, and sodium has always been present in the range of from about 400-700 ppm. Therefore, the lack of sodium in the 6/4 alloy was not only unexpected but an important consideration since sodium may adversely affect the welds of CP titanium.

(23) Other important aspects shown in Table 2 are the percentages of vanadium and aluminum in the 6/4 showing an average of about 5.91% aluminum and about 4.29% vanadium for all of the runs. The runs reported in Table 2 were made with an experimental loop and the valving and control systems for metering the appropriate amount of both vanadium and aluminum were rudimentary. Advanced valving systems have now been installed to control more closely the amount of vanadium and aluminum in the 6/4 produced from the Armstrong Process, although even with the rudimentary control system, the 6/4 alloy was within ASTM specifications. Also of significance is the low iron and chloride content of the 6/4 alloy.

(24) An additional unexpected feature of the 6/4 alloy compared to the CP titanium is the surface area, as determined using BET Specific Surface Area analysis with krypton as the adsorbate. In general, the specific surface area of the 6/4 alloy is much larger than the CP titanium and this also was unexpected. Surface analysis of CP particles which were distilled overnight (about 8-12 hours) between 500-575 C. were 0.534 square meters/gram whereas 6/4 alloy measured 3.12 square meters/gram, indicating that the alloy is significantly smaller than the CP.

(25) The SEMs show that the 6/4 powder is frillier than CP powder, see FIGS. 4-9 and 10-12. As reported by Moxson et al., Innovations in Titanium Powder Processing in the Journal of Metallurgy May 2000, it is clear that by-product fines from the Kroll or Hunter Processes contain large amounts of undesirable chlorine which is not present in the CP titanium powder made by the Armstrong Process (see Table 1). Moreover, the morphology of the Hunter and Kroll fines, as previously discussed, is different from the CP powder made by the Armstrong Process. Neither the Kroll nor the Hunter process has been adapted to produce 6/4 alloy. Alloy powders have been produced by melting prealloyed stock and thereafter using either gas atomization or a hydride-dehydride process (MHR). The Moxson et al. article discloses 6/4 powder made in Tula, Russia and as seen from FIG. 2 in that article, particularly FIGS. 2c and 2d the powders made by Tula Hydride Reduction process are significantly different than those made by the Armstrong Process. Moreover, referring to the Moxson et al. article in the 1998 issue of the International Journal of Powder Metallurgy, Vol. 4, No. 5, pages 45-47, it is seen that the chemical analysis for the pre-alloy 6/4 powder produced by the metal-hydride reduction (MHD) process contains exceptional amounts of calcium and also is not within ASTM specifications for aluminum.

(26) Because the 6/4 alloy made by the Armstrong Process is made without the presence of either calcium or magnesium, these metals should be present, if at all, only in trace amounts and certainly much less than 100 ppm. Sodium which would be expected to be present in significant quantities based on the operation of the Armstrong Process to produce CP titanium in fact is present only at minimum quantities in the 6/4 alloy. Specifically, sodium in the 6/4 alloy made by the Armstrong Process is almost always present less than 200 ppm and generally less than 100 ppm. In some instances, 6/4 alloy has been produced using the Armstrong Process in which sodium is undetectable so that this is a great and unexpected advantage of the 6/4 alloy vis a vis CP titanium made by the Armstrong Process.

(27) Both the Armstrong CP titanium and 6/4 alloy have tap densities or packing fractions in the range of from about 4% to 11%. This tap density or packing fraction is unique and inherent in the Armstrong Process and, while not advantageous particularly with respect to powder metallurgical processing, distinguishes the CP powder and the 6/4 powder made by the Armstrong Process from all other known powders.

(28) As is well known in the art, solid objects can be made by forming 6/4 or CP titanium into a near net shapes and thereafter sintering, see the Moxson et al. article and can also be formed by hot isostatic pressing, laser deposition, metal injecting molding, direct powder rolling or various other well known techniques. Therefore, the titanium alloy powder made by the Armstrong method may be formed into a sintered product or may be formed into a solid object by well known methods in the art and the subject invention is intended to cover all such products made from the powder of the subject invention.

(29) While the invention has been particularly shown and described with reference to a preferred embodiment hereof, it will be understood by those skilled in the art that several changes in form and detail may be made without departing from the spirit and scope of the invention which includes titanium base alloys having lesser amounts of aluminum and vanadium and is specifically not limited to the specific alloys disclosed.